I'm going to make an assumption that you used an adapter to retain the OnStar functions of your vehicle. I just installed in an '08 Silverado and used the PAC OS-04 adapter, but most of them are similar. You also probably had to use the Chime-X module, correct? If so, then you and I will both have to suffer with the annoying turn signals. It's a limitation of using the adapter I think.
I also suspect that your reverse sensors are routing through the Chime-X...and it's not very loud. As of right now, I have no idea how to retain the factory turn signal indicator while using one of th